Happy Fourth of July from Mead O'Brien

"We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness. — That to secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed, — That whenever any Form of Government becomes destructive of these ends, it is the Right of the People to alter or to abolish it, and to institute new Government, laying its foundation on such principles and organizing its powers in such form, as to them shall seem most likely to effect their Safety and Happiness."

THOMAS JEFFERSON, Declaration of Independence

Common Ways to Measure Steam Flow

For steam, energy is primarily contained in the latent heat and, to a lesser extent, the sensible heat of the fluid. The latent heat energy is released as the steam condenses to water. Additional sensible heat energy may be released if the condensate is further lowered in temperature. In steam measuring, the energy content of the steam is a function of the steam mass, temperature and pressure. Even after the steam releases its latent energy, the hot condensate still retains considerable heat energy, which may or may not be recovered (and used) in a constructive manner. The energy manager should become familiar with the entire steam cycle, including both the steam supply and the condensate return.

When compared to other liquid flow measuring, the measuring of steam flow presents one of the most challenging measuring scenarios. Most steam flowmeters measure a velocity or volumetric flow of the steam and, unless this is done carefully, the physical properties of steam will impair the ability to measure and define a mass flow rate accurately.

Steam is a compressible fluid; therefore, a reduction in pressure results in a reduction in density. Temperature and pressure in steam lines are dynamic. Changes in the system’s dynamics, control system operation and instrument calibration can result in considerable differences between actual pressure/temperature and a meter’s design parameters. Accurate steam flow measurement generally requires the measurement of the fluid’s temperature, pressure, and flow. This information is transmitted to an electronic device or flow computer (either internal or external to the flow meter electronics) and the flow rate is corrected (or compensated) based on actual fluid conditions.

The temperatures associated with steam flow measurement are often quite high. These temperatures can affect the accuracy and longevity of measuring electronics. Some measuring technologies use close-tolerance moving parts that can be affected by moisture or impurities in the steam. Improperly designed or installed components can result in steam system leakage and impact plant safety. The erosive nature of poor-quality steam can damage steam flow sensing elements and lead to inaccuracies and/or device failure.

The challenges of measuring steam can be simplified measuring the condensed steam, or condensate. The measuring of condensate (i.e., high-temperature hot water) is an accepted practice, often less expensive and more reliable than steam measuring. Depending on the application, inherent inaccuracies in condensate measuring stem from unaccounted for system steam losses. These losses are often difficult to find and quantify and thus affect condensate measurement accuracy.

Volumetric measuring approaches used in steam measuring can be broken down into two operating designs:

1. Differential pressure
2. Velocity measuring technologies.

DIFFERENTIAL

For steam three differential pressure flowmeters are highlighted: orifice flow meter, annubar flow meter, and spring-loaded variable area flow meter. All differential pressure flowmeters rely on the velocity-pressure relationship of flowing fluids for operation.

Orifice Flow Meter
(courtesy of Foxboro)

Differential Pressure – Orifice Flow Meter

Historically, the orifice flow meter is one of the most commonly used flowmeters to measure steam flow. The orifice flow meter for steam functions identically to that for natural gas flow. For steam measuring, orifice flow flowmeters are commonly used to monitor boiler steam production, amounts of steam delivered to a process or tenant, or in mass balance activities for efficiency calculation or trending.

Differential Pressure – Annubar Flow Meter

The annubar flow meter (a variation of the simple pitot tube) also takes advantage of the velocity-pressure relationship of flowing fluids. The device causing the change in pressure is a pipe inserted into the steam flow.

Differential Pressure – Spring-Loaded Variable Area Flow Meter

The spring-loaded variable area flow meter is a variation of the rotameter. There are alternative configurations but in general, the flow acts against a spring-mounted float or plug. The float can be shaped to give a linear relationship between differential pressure and flow rate. Another variation of the spring-loaded variable area flow meter is the direct in-line variable area flow meter, which uses a strain gage sensor on the spring rather than using a differential pressure sensor.

VELOCITY

The two main type of velocity flowmeters for steam flow, turbine and vortex shedding, both sense some flow characteristic directly proportional to the fluid’s velocity.

Velocity –  Turbine Flow Meter

A multi-blade impellor-like device is located in, and horizontal to, the fluid stream in a turbine flow meter. As the fluid passes through the turbine blades, the impellor rotates at a speed related to the fluid’s velocity. Blade speed can be sensed by a number of techniques including magnetic pick-up, mechanical gears, and photocell. The pulses generated as a result of blade rotation are directly proportional to fluid velocity, and hence flow rate.

Vortex Flowmeter
(courtesy of Foxboro)

Velocity – Vortex-Shedding Flow Meter

A vortex-shedding flow meter senses flow disturbances around a stationary body (called a bluff body) positioned in the middle of the fluid stream. As fluid flows around the bluff body, eddies or vortices are created downstream; the frequencies of these vortices are directly proportional to the fluid velocity.

For more information on process steam management, contact Mead O'Brien by visiting http://www.meadobrien.com or call (800) 892-2769,

Limitorque QX Electronic Actuator User Instructions

Limitorque QX

The Flowserve Limitorque QX quarter-turn smart electronic valve actuator continues the legacy of the industry’s state-of-the-art, non-intrusive, multi-turn MX actuator by including an absolute encoder for tracking position without the use of troublesome batteries. The QX design provides enhanced safety and reduced downtime through improved diagnostics, built-in self-test (BIST) features and LimiGard™ fault protection.

The QX design builds on more than 10 years of experience with proven Limitorque MX technology - the first generation double-sealed electronic valve actuator from Flowserve designed to provide control, ease of use and  accuracy. The QX includes all the user-preferred features of the MX in a quarter-turn smart actuator package. It is the only non-intrusive, double-sealed quarter-turn actuator to display the Limitorque brand.

For more information on any Limitorque actuator, visit Mead O'Brien at http://www.meadobrien.com or call (800) 892-2769.

Limitorque QX Electronic Actuator User Instructions from Mead O'Brien, Inc.

Common Industrial and Commercial Process Heating Methodologies

Fuel boiler producing steam.

Process heating methodologies can be grouped into four general categories based on the type of fuel consumed:

1. Steam
2. Fuel
3. Electric
4. Hybrid systems

These technologies are based upon conduction, convection, or radiative heat transfer mechanisms - or some combination of these. In practice, lower-temperature processes tend to use conduction or convection, whereas high-temperature processes rely primarily on radiative heat transfer. Systems using each of the four energy types can be characterized as follows:

STEAM

Tube heat exchanger.

Steam-based process heating systems introduce steam to the process either directly (e.g., steam sparging) or indirectly through a heat transfer mechanism. Large quantities of latent heat from steam can be transferred efficiently at a constant temperature, useful for many process heating applications. Steam-based systems are predominantly used by industries that have a heat supply at or below about 400°F and access to low-cost fuel or byproducts for use in generating the steam. Cogeneration (simultaneous production of steam and electrical power) systems also commonly use steam-based heating systems. Examples of steam-based process heating technologies include boilers, steam spargers, steam-heated dryers, water or slurry heaters, and fluid heating systems.

FUEL

Fuel-based process heating systems generate heat by combusting solid, liquid, or gaseous fuels, then transferring the heat directly or indirectly to the material. Hot combustion gases are either placed in direct contact with the material (i.e., direct heating via convection) or routed through radiant burner tubes or panels that rely on radiant heat transfer to keep the gases separate from the material (i.e., indirect heating).  Examples of fuel-based process heating equipment include furnaces, ovens, red heaters, kilns, melters, and high-temperature generators.

ELECTRICITY

Electricity-based process heating systems also transform materials through direct and indirect processes. For example, electric current is applied directly to suitable materials to achieve direct resistance heating; alternatively, high-frequency energy can be inductively coupled to suitable materials to achieve indirect heating. Electricity-based process heating systems are used for heating, drying, curing, melting, and forming. Examples of electricity-based process heating technologies include electric arc furnace technology, infrared radiation, induction heating, radio frequency drying, laser heating, and microwave processing.

HYBRID

Hybrid process heating systems utilize a combination of process heating technologies based on different energy sources and/or heating principles to optimize energy performance and increase overall thermal efficiency. For example, a hybrid boiler system may combine a fuel-based boiler with an electric boiler to take advantage of access to lower off-peak electricity prices. In an example of a hybrid drying system, electromagnetic energy (e.g., microwave or radio frequency) may be combined with convective hot air to accelerate drying processes; selectively targeting moisture with the penetrating electromagnetic energy can improve the speed, efficiency, and product quality as compared to a drying process based solely on convection, which can be rate-limited by the thermal conductivity of the material. Optimizing the heat transfer mechanisms in hybrid systems offers a significant opportunity to reduce energy consumption, increase speed/throughput, and improve product quality.

The experts at Mead O'Brien are always available to assist you with any process heating application. Visit http://meadobrien.com or call (800) 892-2769 for more information.

The Basics of a Fieldbus Control Network

Computer systems used within the industrial sector are connected by networks known generally as Fieldbus. Fieldbus systems are a way to connect computers and instruments to a single network in a manufacturing plant and allow for real-time control and monitoring. Fieldbus industrial networks can be broken down into four levels each with increasing levels of complexity.

The most basic level is the sensor bus networks. Sensor bus networks are the least complex of networks developed for industrial application. In these networks, multiple basic field devices like limits witches or level optical sensors are connected to one network cable. The sensor bus network is also capable of transmitting output signals from the controller over one cable to indicator lamps, alarms, or other actuator devices.

The next increasingly complex level of industrial Fieldbus networking is the device bus network. The device bus network is similar in function to the sensor bus network but works on a larger scale connecting many sensors and actuators together. The device bus network also connects equipment to variable speed drives and motor control centers that allow for control of individual elements in the network.

Moving up the pyramid, the next increasing complex level of Fieldbus networking is the control bus network. Control bus networks are the most advanced networks used on the factory floor and data communication happens at a high level. PLC's, or programmable logic controllers, are connected to each other alongside HMI's or human machine interface panels to allow for complete configuration and control of every instrument on the network. Smart instruments, capable of performing complex operations, can also be connected at this network level. For instance, there might be a smart instrument that measures wear and tear on a valve. When the wear reaches a dangerous level it will signal the controller that the valve needs to be replaced.

The enterprise or information level network in a company connects all computers and departments together it is the most overarching and complex of all the various network levels. This level of networking is primarily computer driven which allows for data collection, data monitoring, file transfers, and email exchange on a large scale. The various levels of interconnected Fieldbus networking help to keep industry functioning smoothly and successfully.

Process Instrument Calibration and Repair

The Mead O’Brien Instrument Shop is fully equipped to handle your instrument calibration and repair needs. Whether its repair, calibration or certification services, Mead O’Brien can handle the job. Our technicians are factory trained and certified and can repair and re-calibrate virtually any pressure and temperature transmitter, pressure gauge, pressure switch, thermometer, RTD, or thermocouple.

Industrial Pressure Switches

Industrial Pressure Switch (Ashcroft)

A pressure switch is a device that detects the presence of fluid pressure. Pressure switches use a variety of sensing elements such as diaphragms, bellows, bourdon tubes, or pistons. The movement of these sensors, caused by pressure fluctuation, is transferred to a set of electrical contacts to open or close a circuit.

Normal status of a switch is the resting state with stimulation. A pressure switch will be in its “normal” status when it senses low or minimum pressure. For a pressure switch, “normal” status is any fluid pressure below the trip threshold of the switch.

One of the earliest and most common designs of pressure switch was the bourdon tube pressure sensor with mercury switch. When pressure is applied, the bourdon tube flex's enough to tilt the glass bulb of the mercury switch so that the mercury flows over the electrical contacts, thus completing the circuit. the glass bulb tilts far enough to cause the mercury to fall against a pair of electrodes, thus completing an electrical circuit. Many of these pressure switches were sold on steam boilers. While they became a de facto standard, they were sensitive to vibration and breakage of the mercury bulb.

Pressure Switch Symbols

Pressure switches using micro type electrical switches and force-balanced pressure sensors is another common design.  The force provided by the pressure-sensing element against a mechanical spring is balanced until one overcomes the other. The tension on the spring may be adjusted to set the tripping point, thus providing an adjustable setpoint.

One of the criteria of any pressure switch is the deadband or (reset pressure differential). This setting determines the amount of pressure change required to re-set the switch to its normal state after it has tripped.  The “differential” pressure of a pressure switch should not to be confused with differential pressure switch, which actually measures the difference in pressure between two separate pressure ports.

When selecting pressure switches you must consider the electrical requirements (volts, amps, AC or DC), the area classification (hazardous, non-hazardous, general purpose, water-tight), pressure sensing range, body materials that will be exposed to ambient contaminants, and wetted materials (parts that are exposed to the process media).